In recent years, an increase in inspection sensitivity has been desired in order to detect diseases in an early stage. Therefore, it is important to increase the sensitivity of diagnostic agents. In order to increase the sensitivity of diagnostic agents using a solid phase (e.g., polystyrene plate or magnetic particles), a method that utilizes enzyme coloring has been replaced by a method that utilizes fluorescence or chemiluminescence that achieves higher sensitivity. However, sufficient sensitivity has not been achieved. Specifically, in a diagnosis that detects a specific substance in the presence of biomolecules (e.g., blood serum), a biomolecule, a secondary antibody, a luminescence substrate, and the like are non-specifically adsorbed on a solid phase, an instrument, a container, or the like. As a result, an increase in sensitivity is hindered due to an increase in noise. Therefore, in order to suppress a decrease in sensitivity due to non-specific adsorption of a substance other than the substance showing specific adsorption on a solid-phase surface, an instrument, a container, or the like used for an immunological reaction, a biological substance (e.g., albumin, casein, or gelatin) is normally used for immunoassay as a non-specific adsorption inhibitor to suppress non-specific adsorption and reduce noise.
However, non-specific adsorption still occurs even if the non-specific adsorption inhibitor is added. Moreover, a biological non-specific adsorption inhibitor may cause biological infection (e.g., bovine spongiform encephalopathy (BSE)). Therefore, development of a high-performance, non-specific adsorption inhibitor obtained by chemical synthesis has been desired.
As a non-specific adsorption inhibitor obtained by chemical synthesis, JP-A-10-153599 and JP-A-11-352127 disclose polymers containing polyoxyethylene, and Japanese Patent No. 3443891 discloses a specific methacrylic copolymer. However, these polymers exhibit an insufficient non-specific adsorption inhibition effect.